Since the line passes through the origin, its equation will be like: y = mx
(m = slope of the line)
Angle made by line y = 0.2x will be tan-10.2.
Angle made by required line = twice of above angle = 2tan-10.2
Slope of our line = tan(theta) = tan(2tan-10.2).
Using the property tan2x = 2tanx / (1 - tan2x):
slope = 2tan(tan-10.2) / (1- tan2(tan-10.2) )
Now using the property: tan(tan-1x) = x.
slope = 2(0.2) / (1 - 0.22)
= 0.4 / 0.96
Therefore, Equation of our required line: y = 0.416x